CHEARS

Most people will have experienced a lack of sleep the night before an exam. Some are unable to sleep due to anxiety. Others favor forgoing their sleep for a last minute cramming session. But should we really be doing that? Let us take a look at how sleep impacts memory and learning.

Sleep is defined as a natural and reversible state of reduced responsiveness to external stimuli and relative inactivity, accompanied by a loss of consciousness. There are decades’ worth of research papers on the much studied topic of sleep and memory. These suggest that the quality and quantity of sleep has a profound impact on memory and learning. It is impossible to limit all the findings to a few number of pages – or even a few hundred pages. For the sake of understanding and getting a general picture, let us focus on only a few of these finding.

Initial theories suggested that sleep had a passive role for enhancing memories by protecting them from interfering stimuli. Current theories highlight an active role for sleep in which memories undergo a process of strengthening during sleep.

In general, memory and learning are broken down into three functions:

• Acquisition: Introduction of new information into the brain

• Consolidation: Stabilization of the memory

• Recall: Ability to access the information

Out of these, acquisition and recall take place when we are awake but consolidation is said to take place when we sleep. The exact mechanism behind this consolidation is unknown. However many hypothesis have been put forth on this process. While earlier researches focused on the role of revolving eye movement (REM) sleep, newer research has shown that slow wave sleep (SWS) is equally important and has also pinpointed some electrophysiological, neurochemical and genetic mechanisms for the consolidation of memories.

The synaptic homeostasis hypothesis offers some explanation to this link. While acquiring a memory when we are awake there is an increased synaptic strengthening throughout the brain which increases the cellular need for energy. This is the reason that learning gets saturated after a certain point. During sleep, the increased net synaptic strength gets re-normalized and cellular homeostasis is restored. Thus the burden on the neurons is decreased and it helps in consolidation and integration of memories.

In neurochemical terms, post-learning sleep triggers the calcium-dependent pathway necessary for memory acquisition: systemic electrical reactivation, calcium entry via N-methyl-d-aspartate (NMDA) receptors, kinase and phosphatase activation, early and late gene regulation, synaptic remodeling, as well as neuro-genetic changes. So, the memories processed during sleep may be strengthened, weakened, or restructured.

Putting it in simple terms, sleep detoxifies the brain, replenishes the metabolites and establishes the synaptic homeostasis. Sleep deprivation has a negative impact on memory and functioning as the overworked neurons have difficulty in coordinating the information and hence we find it difficult to access it later. Low quality sleep also negatively affects our mood which also has a consequence in efficient learning. In conclusion, sleep better, learn better.